Power supply control circuit, power supply and power supply control method

ABSTRACT

A power supply control circuit connectable with an input power monitor that monitors an input power value to the power supply, an output power monitor that monitors an output power value from the power supply, and an output power controller that varies the output power value from the power supply, the power supply control circuit having an output power determiner that determines a determined output power value depending on the input power value and a power adjuster that adjusts the output power value to the determined output power value by controlling the output power controller.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims priority of JapanesePatent Application No. 2000-270728 filed Sep. 6, 2000, the contentsbeing incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the invention

[0003] The present invention relates to a power supply control circuit,power supply and power supply control method for converting an existingpower supply at a first voltage and power rating to a secondary voltageand power rating.

[0004] 2. Description of the Related Art

[0005] In a portable electronic device, such as a notebook size personalcomputer, an AC adapter or automobile battery adapter, etc. can be usedfor an external power supply. The automobile battery adapter is called apower supply. The power supply provides an output power by adjusting thepower from the car battery to the power required for the portableelectronic device.

[0006] The capacity of the power supply and the AC adapter generallydetermine the maximum output voltage and the maximum output current.This maximum output voltage and the maximum output current are definedas the rated output. The power supply always operates to compensate tothe rated output even if the input power varies. Therefore, when aninput voltage is high, an input current is small. On the other hand,when an input voltage is low, an input current becomes large.

[0007]FIG. 1 is a schematic diagram of a power supply circuit of therelated art. The circuit includes a noise eliminating filter section 10,a voltage converting section 20 for converting an input power to anoutput power, a rectifying section 30 for rectifying an output of thesecondary side, an output detecting section 40 for monitoring an outputof the secondary side and a coupler 50 for transmitting the condition ofan output detecting circuit in the secondary side to the voltageconverting circuit in the primary side.

[0008] The filter section 10 is formed of a coil LI and a capacitor C1.The filter section 10 is a circuit for preventing propagation of noisegenerated in the voltage converting section 20 to the input side.

[0009] The voltage converting section 20 includes a transformer T1 forvoltage conversion, a transistor Tr1 for shutting off a current flowingthrough the transformer T1 and a control circuit 60 for controlling thetransistor Tr1.

[0010] The rectifying section 30 includes a rectifying diode D1 forrectifying a current outputted from the voltage converting section 20and a capacitor C2 for smoothing the rectified current.

[0011] The output detecting section 40 includes a sense resistor R0 fordetecting an output current value of the power supply and a sensecircuit 70 for detecting a voltage value across both ends of the senseresistor R0.

[0012] The coupler 50 is a circuit for transmitting an output of thesense circuit 70 to the control circuit 60. In the coupler 50, aphoto-coupler is used in general to electrically insulate the primaryside and secondary side.

[0013] In FIG. 1, when the transistor Tr1 is ON, an input current flowsin the primary side coil of the transformer T1. When the transistor Tr1is OFF, an output current flows in the secondary side of the transformerT1. The circuit explained above is defined as an RCC type switchingregulator.

[0014] In the RCC type switching regulator, when an output voltage valueis Vout, input voltage value is Vin, the ON time of transistor Tr1 isTon and the OFF time of transistor Tr1 is Toff, the relationship isdefined by Vin×Ton=Vout×Toff. However, when the number of turns of theprimary coil of the transformer T1 is assumed to be identical to thenumber of turns of the secondary coil, this formula can be modified sothat Vout=(Vin×Ton)/Toff. Moreover, it can be modified by the period ofON/OFF of the transistor Tr1 replacing T, producingVout=(Vin×Ton)/(T−Toff).

[0015] As indicated in the above formula, the input current can beadjusted by controlling the ON time of transistor Tr1 while the outputvoltage is kept constant. Thus, even when the load connected to theoutput terminal of the power supply varies, the value of Vout can bemaintained constant using the feed-back control that controls the ONtime of the transistor Tr1 by monitoring the output voltage Vout.

[0016]FIG. 2 is a schematic diagram of another power supply circuit ofthe related art. The circuit of FIG. 2 is different from the RCC typeswitching regulator in that the voltage converting and rectifyingsection 80 is formed by integrating the voltage converting section 20and rectifying section 30 of FIG. 1. Rectifying section 80 is thereforeprovided in place of individually providing a voltage converting sectionand a rectifying section.

[0017] In FIG. 2, when the transistor Tr1 is ON, an input current flowsthrough the primary side coil of the transformer T1. This causes theoutput current to flow through the secondary side coil of thetransformer T1. This type of circuit is defined as a FORWARD typeswitching regulator.

[0018] In FIG. 2, the transformer T1 operates as a switch circuit. Thetransformer T1 does not operate as a voltage converting circuit.Therefore, a choke coil L2 and a flywheel diode DO are required forvoltage conversion in addition to the transformer T1. In the circuit ofFIG. 2, the relationship of the voltage to the time the transformer T1is ON is Vout=(Vin×Ton)/(Ton+Toff)=(Vin×Ton)/T.

[0019] In addition, the current flowing through L2 also flows in theoutput detecting section 40 and the noise eliminating filter section 10while the transistor Tr1 is ON. Moreover, current flowing through L2 issupplied via D1 while the transistor Tr1 is OFF. Therefore, an averageinput current Iin to the power supply circuit becomes equal to a productof an output current lout and the ON time of transistor Trn.Accordingly, the relationship of current to the time transistor Tr1 isON is Iin=(lout×Ton)/T.

[0020] As indicated in the above formula, controlling the ON time of thetransistor Tr1 can cover variation of the input voltage. Moreover, evenwhen the capacity of the load connected to the output of the powersupply is varied, Vout can be maintained constant by having the feedbackcontrol vary the ON time of the transistor Tr1 in accordance with theoutput voltage Vout.

[0021]FIG. 3 is a schematic diagram illustrating details of the sensecircuit 70 and control circuit 60 that monitor the output power in thecircuit illustrated in FIG. 1 or FIG. 2. The sense circuit 70 includes avoltage amplifier AMP11, a couple of error amplifiers ERA11, ERA12 andreference voltage sources e11, e12. The control circuit 60 includes atriangular wave oscillator 66, a PWM comparator 62 and a drive circuit68.

[0022] The reference voltage source e11 is the reference voltage used todetermine the output current value. The reference voltage source e12 isthe reference voltage used to determine the output voltage value.

[0023] The voltage amplifier AMP11 measures a voltage drop generated bya current flowing through the sense resistor R0. The voltage amplifierAMP11 outputs a voltage that is proportional to a current value flowingthrough the sense resistor R0. The error amplifier ERA11 compares anoutput voltage value with the reference voltage value e11. The erroramplifier ERA11 outputs a low level when a large current flows throughthe sense resistor R0 or a high level when a small current flows throughthe sense resistor R0.

[0024] Similarly, the error amplifier ERA12 compares an output voltagevalue of the power supply with the reference voltage value e12. Theerror amplifier ERA12 outputs a low level when the power supply outputsa high output voltage value or a high level when the power supplyoutputs a low output voltage value.

[0025] The PWM comparator 62 is a voltage comparator including oneinverting input and a plurality of non-inverting inputs. Namely, the PWMcomparator 62 illustrated in FIG. 3 is a voltage pulse width converterfor controlling the ON time of an output pulse depending on an inputvoltage value. The PWM comparator 62 compares the minimum voltage valueamong a plurality of non-inverting inputs shown by a +, with the voltagevalue of an inverting input shown by a −. The PWM comparator 62 providesan output when the voltage value of inverting input is lower. An outputsignal from the triangular wave oscillator 66 is inputted to theinverting input of the PWM comparator 62. Meanwhile, the output from theerror amplifier ERA11 and the output from the ERA12 are inputted to thenon-inverting input.

[0026] During the period where the triangular wave voltage value fromthe triangular wave oscillator 66 is lower than the output voltage oferror amplifier ERA11 and is also lower than the output voltage value ofthe error amplifier ERA12, an output voltage from the PWM comparator 62is inputted to the drive circuit 68. With this input, the drive circuit68 is driven to drive the switching transistor Tr1 of the power supply.Moreover, during the period where the triangular wave voltage value fromthe triangular wave oscillator 66 is higher than the output voltagevalue of the error amplifier ERA11 or the triangular wave voltage valuefrom the triangular wave oscillator 66 is higher than the output voltagevalue of the error amplifier ERA12, an output is not provided to thedrive circuit 68 from the PWM comparator 62. Thereby, drive of the drivecircuit 68 stops and the switching transistor Tr1 of the power supplyturns OFF.

[0027] As explained above, the switching transistor Tr1 is turned OFFdepending on the output voltage value of the power supply that isdetected with the sense circuit 70. The power supply control circuitcontrols an output voltage and an output current of the power supplywith the structure explained above.

[0028] In FIG. 3, an output from the sense circuit 70 for monitoring anoutput voltage and an output current is then inputted directly to thePWM circuit 62 of the control circuit 60. However, if electricalisolation is required between the sense circuit 70 and the controlcircuit 60, a photocoupler is connected to each input end of the PWMcircuit 62. Such electrical isolation can also be realized by attachinga photocoupler to the output of the sense circuit 60.

[0029] In the circuit illustrated in FIG. 3, the PWM comparator 62selects a lower voltage value among the outputs of the error amplifiersERA11 and ERA12. However, it is also possible that the sensor circuit 60combines the output voltages of the error amplifiers ERA11 and ERA12 andtransmits only the lower voltage value.

[0030]FIG. 4 is a schematic diagram illustrating a circuit to realizesuch modification. The circuit illustrated here is an analog circuit totransmit the lower voltage value among the outputs of the erroramplifiers ERA11 and ERA12. When a voltage of the error amplifier ERA11becomes high, the base potential of the transistor Tr11 becomes high anda base current is reduced. Therefore, a collector resistance of Tr11becomes high and a constant current is supplied to the collector of Tr1from the constant current source i. Therefore, the collector voltage ofTr11 becomes higher as the collector resistance of Tr11 becomes large.

[0031] When the voltage of error amplifier ERA11 becomes low, a basepotential of Tr11 becomes low. Therefore, since a base currentincreases, a collector resistance of Tr11 becomes small. Since aconstant current is supplied to the collector of Tr11 from the constantcurrent source i, a collector voltage of Tr11 becomes low in proportionto reduction of the collector resistor of Tr11.

[0032] Similarly, when a voltage of the error amplifier ERA12 becomeshigh, a base potential of Tr12 becomes high. Thereby, since a basecurrent is reduced, a collector resistance of Tr12 becomes large. Aconstant current is supplied to the collector of Tr12 from the constantcurrent source i. Accordingly, a collector voltage of Tr12 becomes highin proportion to increase of collector resistance of Tr12.

[0033] When a voltage of the error amplifier ERA12 becomes lower, a basepotential of Tr12 becomes low. If so, since a base current increases, acollector resistance of Tr12 becomes small. Since a constant current issupplied to the collector of Tr12 from the constant current source i, acollector voltage of Tr12 becomes low in proportion to reduction ofcollector resistance of Tr12.

[0034] The collectors of Tr11 and Tr12 are connected to the commonconstant current source i. Therefore, the collector voltage of Tr11 andTr12 is fixed to the lower voltage. Accordingly, a lower voltage of theoutput voltage of error amplifier ERA11 or the output voltage of erroramplifier ERA12 is outputted as the collector voltage of Tr11 and Tr12.

[0035]FIG. 7 is a structural diagram illustrating a related art externalpower supply that is connected to an electronic device with the powersupply. In this figure, a docking station 130 is connected as a new loadbetween the external power supply 100 and electronic device 110.

[0036] In FIG. 7, the power inputted from the external power supply 100is supplied as the power source of the electronic device 110. Moreover,when a secondary battery 111 is provided within the electronic device110, such power is also supplied as the charging power of the secondarybattery 111. The power supplied to the electronic device 110 isconverted to the voltage value required by the device with a voltageconverting circuit 112.

[0037] The secondary battery 111 is a built-in battery to supply thepower to the electronic device 110 when the power source from theexternal power supply 110 stops. Power supply 150 applies the power tocharge the secondary battery 111 built in the electronic device. Amicrocomputer 113 detects start and end of charging at the time ofcharging the secondary battery 111. The microcomputer 113 controls theON/OFF condition of the power supply from a charger and also controlsthe power supply.

[0038] Voltage comparator COMP101 detects that the power is suppliedfrom the external power supply. COMP101 sends a high level to themicrocomputer when a voltage value measured with voltage dividingresistors R103 and R104 is higher than reference voltage value el.AMP101 measures a current value supplied to the secondary battery 111from the power supply 150. A diode D101 prevents leak of power of thesecondary battery 111 to the external circuit. A diode D102 preventsdirect application of the power from the external power supply to thesecondary battery 111 when the power is supplied from the external powersupply.

[0039] The power supply 150 is a DC-DC converter to generate a constantvoltage or a constant current or a constant voltage current. The powersupply 150 includes a sense resistor R101 for measuring an input currentvalue from the external power supply, a sense resistor R102 formeasuring a charting current value of the secondary battery 111, a mainswitch transistor FET101, a choke coil L101, a flywheel diode D103, asmoothing capacitor C101 and a control circuit. Detailed operation ofthe power supply 150 is not explained here, because it is similar to theoperation explained above.

[0040] The docking station 130 is provided to expand the functions ofthe electronic device 110. This docking station 130 can expand thefunctions of the electronic device through connection with theelectronic device. Portability is a very important factor in theportable type information device, such as a notebook size personalcomputer.

[0041] Therefore, the basic section of the notebook size personalcomputer must be given the required minimum functions through reductionin size and weight as much as possible. For this reason, the LANconnecting mechanism which cannot be used during the transportation andCD drive or DVD drive which is not used frequently are no longer loadedto the body of notebook size personal computer. Meanwhile, it is veryconvenient when various functions are provided in the notebook sizepersonal computer for when it is used on the desk. Therefore, thedocking station is provided with high level functions. Connecting anotebook size personal computer to the docking station can attainexpandability for use of various devices.

[0042] In FIG. 7, the external power supply 100 sends the power to bothelectronic device 110 and docking station 130. When the secondarybattery 111 is charged in the side of electronic device 110, the powersupply 150 tries to extract the maximum current specified at the time ofdesign from the external power supply 100. However, the power ofexternal power supply 100 is also supplied to the docking station 130.Accordingly, the external power supply 100 enters the over-loadcondition and thereby shuts off the output.

[0043] Therefore, the external power supply 100 for docking station 130shall have the capacity to cover the addition of the maximum currentused for the docking station 130 to the power consumption of theelectronic device 110.

[0044] However, in this case, if a load current, for example, of thedocking station 130 is reduced depending on the operating condition, anextra power cannot be used as the charging power of the secondarybattery in the side of electronic device 110.

[0045] As a method of overcoming such problem, there is proposed acharging control circuit (Japanese Published Unexamined PatentApplication No. HEI 10-286586) for keeping constant the output voltageof external power supply and controlling the charging current bymonitoring an output voltage value of the external power supply.However, this circuit cannot attain the result as expected when anoutput power value of external power supply does not conform to thetheoretical value.

SUMMARY OF THE INVENTION

[0046] First, in accordance with the present invention, a power supplycan attain a maximum output while preventing damage to an external powersupply even when the external power supply needs to provide varyingoutput voltage. Therefore, additional output can be provided forportable electronic terminals. Thus, the exemplary embodiments as notedherein help solve the tendency to increase power consumption. Inaddition, it is possible to provide a means for safely and efficientlyconsuming additional power when a new load is connected between theexternal power supply and the power supply.

[0047] For example, FIG. 15 shows that the exemplary external powersupply drops the input voltage and increases the input current whenoverloaded and protects its output current as much as possible whenoverloaded. However, a power supply of lower reliability shown in FIG.18 lowers the voltage when overloaded but sometimes provides anexcessive output power. If this condition is continued for a long time,the external power supply will probably over-heat.

[0048] One exemplary embodiment is provided with a mechanism to monitorthe input power value (input voltage and input current) of the chargerand therefore it can determine, if the external power supply cannotsupply the charging power to the receiving device, whether the cause isa limitation in the input current or in the input voltage. Therefore,the exemplary power supply does not become overloaded and can optimizethe charging condition.

[0049] Moreover, it is possible to avoid erroneous recognition for theend of charging because of insufficient input power, even when a lithiumion (Li+) battery is used to complete the charging when the chargingcurrent value becomes the predetermined constant value or less.

[0050] The principles of the present invention have been explained abovewith an example of a car battery adapter in view of easily helping theunderstanding of the present invention. It is obvious that the presentinvention is useful not only for the car battery adapter but for manyother similar power supply devices. The present invention can be used inany power supply circuit to convert an input voltage from a externalpower supply to a predetermined power. The present invention hasparticular effect in a condition where the voltage of external powersupply is unstable. For example, in a certain region, the presentinvention can provide sufficient effect on the adapter connected to thecommercial power supply.

[0051] Moreover, other exemplary embodiments can be used as the chargingcircuit for the battery within an electronic device and can provide theincreased current for portable type electronic devices, assuringportability and sophisticated functions. For example, the presentinvention can provide sufficient effect to the portable type terminalthat is used in connection with the so-called docking station and isalso used, when it is carried, by separating only the body provided withthe required minimum functions from the docking station.

[0052]FIG. 5 illustrates an output characteristic of the power supplyillustrated in FIG. 1. The rated output of this adapter is 16 volts/3.5amperes. The output voltage of 16 volts is adjusted with the referencevoltage e12 of the sense circuit 60. An output current of 3.5 amperes isadjusted with the reference voltage e11 of the sense circuit 60.

[0053] Here, it is assumed that a load connected to this adapteroverloads its capacity by requiring an output current of 3.5 amperes ormore. Even in such a case, the rated output of the adapter is 16volts/3.5 amperes and therefore the output current of this adaptershould not exceed 3.5 amperes under normal conditions.

[0054]FIG. 6 illustrates the relationship between an input current andan input voltage of an ideal power supply. Here, the voltage conversionefficiency of the power supply is assumed as 80%. This figure indicatesthe input current value and input voltage value when the rated output of3.5 amperes is provided. When a battery voltage of a car is 12 volts orhigher, the input current is 6.0 amperes or less. However, when thebattery voltage of a car is lowered to 9 volts or less, the inputcurrent becomes 8.0 amperes.

[0055] When the related art power supply is connected to the carbattery, such as through an automobile battery adapter, it is generallyconnected to the terminal of a cigarette lighter of a car. In thereceptacle circuit of the cigarette lighter, a fuse of about 10A isinserted to prevent short-circuiting the battery. When a fuse is used inthe rated condition, it is known that the fuse blows usually after twohours. In order to prevent blowout of the fuse, a current flowingthrough the fuse must be set 80% or less of the rated current.Therefore, when a related art power supply as shown in FIG. 1 is used,it is required to set the current input to the related art power supplyto 8 amperes or less.

[0056] Moreover, it is also required to insert a protection fuse withinthe automobile battery adapter itself in order to avoid blow-out of thecar fuse due to a short-circuit of the power supply. Namely, even when ashort-circuit internal to the power supply is generated, the fuse withinthe power supply must blow out before the fuse of an automobile. Thus,most power supply adapters for use in automobiles use a fuse rated at 8amperes.

[0057] However, as explained above, the fuse generally blows out aftertwo hours when the current flows in its rated capacity. Therefore, it isrequired to limit an input current of the automobile battery adapter to6A in order to provide adequate safety when the automobile adapter isused continuously.

[0058] On the other hand, when the performance of car battery isdeteriorated or charging is insufficient, the output voltage of thebattery is reduced, in some cases to 9 volts or less. The voltage valueof about 9 volts is used because it is near to the limit value of thevoltage required to start the engine.

[0059] Therefore, using the worst case, an input power to be inputted tothe power supply becomes 9V/6 A (6 A×9V=54 watts (W)). When theconversion efficiency of automobile battery adapter is assumed as theordinary value of 80%, an output voltage from the automobile batteryadapter becomes equal to 54 W×0.8=43.2 W.

[0060] In recent years, power consumption by electronic devices hasincreased. For example, an exemplary hand-held terminal requires theoccasional input of 70 W. Therefore, the automobile battery adapter thatcan output only the power of about 43 W or so has insufficient capacity.When the device therefore attempts to draw sufficient current tooperate, an input current of the power supply increases and therebyblows-out the fuse.

[0061] The automobile battery adapter has been explained above as asimple example, but an additional exemplary problem lies in generatingdamage to the electric circuits due to excessive input current as wellas in the automobile battery adapter in the environment that the inputpower becomes unstable.

[0062] In exemplary embodiments of the present invention as will bedescribed below, a structure for monitoring an input power value to thepower supply is added to the structure of the power supply controlcircuit of the related art. Thereby, it is possible to control the inputcurrent to a value lower than the fuse value without adjusting forvariation of input voltage in the power supply control circuit.Therefore, the exemplary power supply using a power supply controlcircuit in accordance with the present invention can prevent overcurrent being outputted to an external power supply.

[0063] Moreover, exemplary embodiments of the present invention as willbe described below provide a power supply which outputs the rated powerwhen an input voltage is normal. However, when an input voltage from theexternal power supply is low, the power outputted from the power supplyis reduced. Therefore, the power supply can control an excessive currentinput from the external power supply.

[0064] Moreover, exemplary embodiments of the present invention as willbe described below provide a power supply control circuit, which canoutput the rated power of the fuse for a constant period and thereafterreduce the output power when the input voltage from the external powersupply is low. Therefore, the exemplary power supply using the powersupply control circuit of the present invention can control input ofexcessive current from the external power supply. Moreover, even when anew load is connected between the external power supply and hand-heldmobile terminal, the external power can be used effectively.

[0065] In order to achieve various advantages as noted and in accordancewith embodiments of the present invention, there is provided a powersupply control circuit connectable with an input power monitor thatmonitors an input power value to the power supply, an output powermonitor that monitors an output power value from the power supply, anoutput power controller that varies the output power value from thepower supply and a power supply control circuit connected to the inputpower monitor, the output power monitor and the output power controller,the power supply control circuit having an output power determiner thatdetermines a determined output power value depending on the input powervalue and a power adjuster that adjusts the output power value to thedetermined output power value by controlling the output powercontroller.

[0066] As embodied herein, this circuit preferably has a first timerthat measures passage of a first time a second timer that measurespassage of a second time after the first timer measures the first timeand an output power switch that instructs the first value to the outputpower determining section while the first timer measures passage of thefirst time, and instructs the second value to the output powerdetermining section while the second timer measures passage of thesecond time.

[0067] In accordance with further embodiments of the present invention,there is provided a power supply, having an input power monitor thatmonitors an input power value, an output power monitor that monitors anoutput power value an output power controller that varies the outputpower value by controlling an input current value an output powerdeterminer that determines a determined output power value depending onthe input power value notified from the input power monitor and a poweradjuster that maintains the output power value notified from the outputpower monitor as the determined output power by controlling the outputpower controller.

[0068] As embodied herein, this circuit preferably has a first timerthat measures passage of a first time a second timer that measurespassage of a second time after the first timer measures the first timeand an output power switch that instructs the first value to the outputpower determining section while the first timer measures passage of thefirst time, and instructs the second value to the output powerdetermining section while the second timer measures passage of thesecond time.

[0069] In accordance with further embodiments of the present invention,there is provided a power supply control method that includes outputtinga first output power value in which an input current value becomes afirst value for a first time period by controlling the input currentvalue so that an output power is maintained as the first output powervalue and outputting a second output power value that is smaller thanthe first output power value for a second time period by controlling theinput current value so that the output power is maintained as the secondoutput power value.

[0070] In accordance with further embodiments of the present invention,there is provided an output power controller having an output powerdeterminer that determines a determined output power value depending onan input power value and a power adjuster that adjusts the output powervalue to the determined output power value by controlling an inputcurrent value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] These and other objects and advantages of the present inventionwill become more apparent and more readily appreciated from thefollowing description of the preferred embodiments, taken in conjunctionwith the accompanying drawings of which:

[0072]FIG. 1 is a structural diagram illustrating a related art powersupply;

[0073]FIG. 2 is a structural diagram illustrating another related artpower supply;

[0074]FIG. 3 is a structural diagram illustrating a related art powersupply control circuit;

[0075]FIG. 4 is a structural diagram illustrating another related artpower supply control circuit;

[0076]FIG. 5 is a graph illustrating input characteristics of a relatedart power supply;

[0077]FIG. 6 is a graph illustrating output characteristics of an idealpower supply;

[0078]FIG. 7 is a diagram illustrating a structure of a related artpower supply wherein a docking station is used;

[0079]FIG. 8 is a structural diagram illustrating a power supply inaccordance with an embodiment of the present invention;

[0080]FIG. 9 is a diagram illustrating a power supply control circuit inaccordance with an embodiment of the present invention;

[0081]FIG. 10 is a diagram illustrating a power supply control circuitin accordance with an embodiment of the present invention;

[0082]FIG. 11 is a diagram illustrating a power supply in accordancewith an embodiment of the present invention;

[0083]FIG. 12 is a diagram illustrating a power supply control circuitin accordance with an embodiment of the present invention;

[0084]FIG. 13 is a diagram illustrating a power supply control circuitused in a power supply in accordance with an embodiment of the presentinvention;

[0085]FIG. 14 is a graph illustrating input characteristics of a powersupply in accordance with an embodiment of the present invention;

[0086]FIG. 15 is a graph illustrating output characteristics of a powersupply in accordance with an embodiment of the present invention;

[0087]FIG. 16 is a graph illustrating voltage control of a power supplycontrol circuit in accordance with an embodiment of the presentinvention;

[0088]FIG. 17 is a graph illustrating current control of a power supplycontrol circuit in accordance with an embodiment of the presentinvention; and

[0089]FIG. 18 is a graph illustrating output characteristics of anexternal power supply in lower performance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0090] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals refer to likeelements throughout.

[0091]FIG. 8 illustrates a first exemplary embodiment of a power supplycircuit in accordance with the present invention. Voltage convertingsection 25 of the first exemplary power supply circuit is different fromthe circuit of the related art. In the first exemplary power supply, acurrent sense resistor R1 measures an input current value that is addedto the related art power supply. Both ends of sense resistor R1 areconnected to a control circuit 65. Similar elements are designated withthe same reference numerals of FIG. 1 and operate in a similar samemanner are not explained here.

[0092]FIG. 9 illustrates details of the sense circuit 70 of the outputdetecting section 40 and the control circuit 65 of the voltageconverting section 25. Explanation of the part of sense circuit 70 ofFIG. 9 that is similar to that in the related art is omitted here.

[0093] In the control circuit 65 of FIG. 9, e21 is the reference voltageused to determine an input current value. AMP21 measures a voltage dropgenerated by a current flowing through the current sense resistor R1.AMP21 outputs a voltage in proportion to a current value followingthrough the sense resistor R1. ERA21 compares an output voltage value ofthe voltage amplifier AMP11 with the reference voltage value e21. When acurrent flowing through the sense resistor R21 is high, the erroramplifier ERA21 outputs a low level signal. When the current flowingthrough the sense resistor R1 is small, the error amplifier ERA21outputs a high level signal.

[0094] An output of ERA21 is impressed to the non-inverting input of thePWM comparator 67. Therefore, during the period where a triangular wavevoltage value outputted from the triangular wave oscillator 66 is lowerthan any output voltage value of the error amplifier ERA21 and sensecircuit 70, the drive circuit 68 is driven. Thereby, the switchingtransistor Tr1 (FIG. 8) turns ON. Moreover, during the period where thetriangular wave voltage value from the triangular wave oscillator ishigher than any one of the output voltage value of the sense circuit 70and error amplifier ERA21, the drive circuit 68 is driven. Thereby, theswitching transistor Tr1 (FIG. 8) turns OFF.

[0095]FIG. 15 illustrates how in the first exemplary power supply, evenif an input voltage to the power supply is lowered, the output currentvalue never exceeds the predetermined constant value. Therefore, thefirst exemplary power supply can prevent breakdown of the circuit due toover-current conditions.

[0096]FIG. 13 illustrates a second exemplary embodiment of a powersupply circuit in accordance with the present invention. The secondexemplary embodiment is capable of outputting the rated voltage andcurrent when the input voltage value is higher and the input currentvalue is equal to the specified value or less. However, when the inputvoltage value to the power supply is low and the input current valuebecomes equal to the specified value or more, an output current islowered.

[0097] Even though the second exemplary embodiment does not protect theoutput power, it is still effective. Not all devices require full powerall the time. In addition, in other devices, reduced power for shortperiods of time does not negatively impact operation. In addition,protecting the input power is advantageous given the additional powerpossible because of the properties of the fuse as noted above.

[0098] The power supply circuit illustrated in FIG. 9 measures a voltagedrop generated with a current flowing through the resistor R1 andthereby controls an output by utilizing a current sense resistor R1. Thepower supply circuit illustrated in FIG. 10 illustrates a structure tocontrol the output by measuring an input voltage value in place of thepower supply circuit explained above.

[0099] In the power supply control circuit 165 of FIG. 10, the voltagedividing resistors R21 and R22 for measuring input voltage are providedin place of the current sense resistor R21 and voltage amplifier AMP21.An output of the voltage dividing resistor R21 is inputted to the erroramplifier ERA121. Thereby, an output of the voltage dividing resistorR21 is compared with the reference voltage value e21. A voltage isoutputted from the error amplifier ERA121 depending on the outputvoltage value of the voltage dividing resistor R21.

[0100] When the input voltage value measured with the voltage dividingresistor sense resistors R21 and R22 is high, the error amplifier ERA121outputs a high level signal. When the input voltage value measured withthe voltage dividing resistor sense resistors R21 and R22 is low, theerror amplifier ERA121 outputs a low level signal.

[0101] An output of ERA121 is applied to the non-inverting input of thePWM comparator 167. Therefore, the drive circuit 168 is driven duringthe period where the triangular wave voltage value from the triangularwave oscillator 169 is lower than the output voltage value from thesense circuit 70 and is lower than the output voltage value from theerror amplifier ERA121. Thereby, the switching transistor Trn turns ON.Moreover, the drive of the drive circuit 168 is stopped during theperiod where the triangular wave voltage value from the triangular waveoscillator 169 is higher than the output voltage value from the sensecircuit 70 or the triangular wave voltage value is higher than theoutput voltage value of the error amplifier ERA121. Thereby, theswitching transistor Tr1 turns OFF.

[0102]FIG. 14 shows characteristics of the fuse located prior to theabove exemplary power supply circuit. As is already explained above, itis known that the fuse is generally blown out after two hours when it isused under the rated current condition. Therefore, it is designed, thata current exceeding 80% of the rated current does not flow into thefuse. However, in accordance with the present invention, the followinginformation has been obtained as a result of detailed investigation ofthe characteristics of fuses.

[0103] Namely, a current of 8 amperes is applied continuously for 54minutes to the fuse having the rated power of 8 amperes. Thereafter, acurrent of 6 amperes is applied for six minutes to such fuse. When suchcontrol is repeated, the fuse has not blown out even after thecontinuous operation of 1000 hours. Moreover, there are no changesobserved in the resistance value of the fuse itself.

[0104] In other words, blow-out of the fuse can be preventedindefinitely by keeping, during continuous operation, the power level atthe rated capacity for 90% of the operational time and also keeping thepower level at 80% of rated capacity for 10% or more of the operationaltime.

[0105]FIG. 11 is an exemplary embodiment of a power supply in accordancewith the invention based on the result explained above. The power supplycomprising this power supply circuit is also provided with a 8ampere-fuse in order to keep the input current from the battery within 8ampere. However, since it is possible to apply the current of 8 amperefor the time of 90% of the usage time, an output of 72 W can be attainedduring this period. Accordingly, this power supply can realizeconnection of a variety of electronic devices, such as a hand-heldinformation terminals, requiring large consumption of power that will beused in the near future.

[0106] In FIG. 11, the voltage amplifier AMP21, error amplifier ERA21and PWM comparator 67, etc. are similar to those of the power supplycircuit illustrated in FIG. 8 and operate in a similar manner.

[0107] In the power supply circuit of FIG. 8, a kind of referencevoltage value of the error amplifier ERA21 is used for controlling aninput current. However, in the circuit of the power supply of FIG. 11,two kinds of voltages, e31 and e32, are switched with the switch circuitSW31. Therefore, the current value inputted to the power supply may bemaintained at any one of two values. As these two kinds of currentvalues, the voltage value e31, for example, keeps the input voltage to 6amperes, while the voltage value e32 keeps the input voltage to 8amperes.

[0108] The voltage comparator COMP31 detects that a current flowing intothe current sense resistor R1 is higher than the value corresponding tothe first reference voltage value e31. The voltage comparator COMP31outputs a high level when the input current value is higher than thevalue corresponding to the first reference voltage value. The voltagecomparator COMP31 outputs a low level when the input current value islower than the value corresponding to the first reference voltage value.

[0109] FET31 is a switch circuit that is controlled for ON and OFF withan output of the voltage comparator COMP31. Variable i designates aconstant current source to charge a capacitor C31. A resistor R33 is adischarging resistor for discharging the capacitor C31. The voltagecomparator COMP32 compares a voltage value of the capacitor C31 with thereference voltage value e33.

[0110] The voltage comparator COMP32 outputs a high level when thevoltage value of C31 is higher than the reference voltage value e33. Anoutput from the voltage comparator COMP32 causes the error amplifierERA31 to select the reference voltage value e31 via the switch SW31.When the voltage value of C31 is lower than the reference voltage e33,the voltage comparator COMP22 outputs a low level signal. An output ofthe voltage comparator COMP32 causes the error amplifier 31 to selectthe reference voltage value e32 via the switch SW31.

[0111] In the power supply circuit of FIG. 13, when an input currentvalue to the power supply is lower than the value corresponding to thefirst reference voltage value e31, the voltage comparator COMP31continuously outputs a low level signal. Therefore, the voltage value ofcapacitor C31 is kept low. Accordingly, the voltage comparator COMP32continuously outputs a low level signal. After all, the referencevoltage value of the error amplifier ERA31 is set to the secondreference voltage value e32. An input current to the power supply isallowed to have the value corresponding to the second reference voltagevalue.

[0112] When an input current to the power supply increases and exceedsthe current value corresponding to the first reference voltage valuee31, the voltage comparator COMP31 outputs a high level. An output ofthe voltage COMP31 charges the capacitor C31 by turning ON FET31. Thecapacitor C31 is charged only when the input current value of the powersupply is higher than the current value corresponding to the firstreference value. When the input current value of the power supply islower than the current value corresponding to the first reference value,the capacitor C31 is never charged.

[0113] A voltage value of the capacitor C31 rises therefore inproportion to the time where the input current value of the power supplyis higher than the current value corresponding to the first referencevoltage value. The voltage comparator COMP32 compares the voltage valueof capacitor C31 with the reference voltage value e33. Therefore, whenthe total sum of the time where the input current value to the powersupply is higher than the current value corresponding to the firstreference voltage value becomes longer than the time designated with thereference voltage value e33, the voltage comparator COMP32 outputs ahigh level. An output of the voltage comparator COMP32 sets thereference voltage value of the error amplifier ERA31 to the firstreference voltage value e31. Since the reference voltage value of theerror amplifier ERA31 is varied to the first reference voltage value, aninput current of the car adapter is limited to the value lower than thecurrent value corresponding to the first reference voltage value.

[0114] While the voltage value of capacitor C31 is higher than thereference voltage value e33, the voltage comparator COMP32 continuouslyoutputs a high level. However, the voltage value of output capacitor C31is discharged via a discharging resistor R33. Therefore, after theconstant time determined with the capacitance value of the capacitor C31and a value of the discharging resistor R33, the voltage value ofcapacitor C31 becomes lower than the reference voltage value e33. Thevoltage comparator COMP32 outputs a low level to set the referencevoltage value of the error amplifier ERA31 to the second referencevoltage value e32.

[0115] In the above explanation, the control circuit selectively usestwo kinds of current value for simplifying the explanation. However, inactual use, these current values may be continuously varied betweenthese two kinds of values. In this case, it is required to set in moredetail the relationship between the current value and passage of time.For this purpose, the power supply circuit may be structured bycombining a known power supply circuit structure with a power supplycircuit in accordance with the present invention. In any case, when thecurrent flows continuously to the fuse at the rated capacity for amaximum period of 108 minutes (90% of two hours) and the current flowingin the fuse is set to 80% of the rated capacity for the remaining 12minutes of two hours.

[0116] It is preferable that the time when the current of the ratedcapacity flows into the fuse is set to the period within 54 minutes (90%of an hour) and the current flowing into the fuse is set to 80% of therated capacity for the remaining six minutes of an hour. Thus, even whenthe power supply has been designed as explained above, assumingpreviously an output value of the external power supply, it is alsopossible to connect another load between the external power supply andpower supply.

[0117]FIG. 11 is a circuit diagram illustrating the second exemplaryembodiment of the present invention in such a case that a new load isconnected between the external power supply and the portable typeelectronic device.

[0118] In the power supply of this embodiment, an input currentnotification line and an input power notification line to the controlsection 215 from the microcomputer 213 are newly added in comparisonwith the related art power supply circuit illustrated in FIG. 7. Aninput current notification line to the microcomputer 213 from thecontrol section 215 and the MASK signal line are also added. Content andprocedure for these signals will be explained later.

[0119] Microcomputer 213 is a micro-controller to control the powersupply, and is connected with power supply 250. The microcomputer 213can detect MASK1 signal and MASK2 signal from the power supply 250 andan input current value to the power supply 250.

[0120]FIG. 12 is a diagram illustrating the control section 215 of thepower supply circuit of FIG. 11. The control section 215 comprises areference voltage source e211 for setting the upper limit of the currentvalue flowing into the sense resistor R210 and a reference voltagesource e221 for monitoring the voltage when the external power supplydroops or drops the voltage under the overload condition.

[0121] R211 and R212 are divided resistors for measuring the voltagevalue of the external power supply 100 inputted to the power supply 250.e212 is the reference voltage for comparing the input voltage value ofthe power supply 250. ERA212 amplifies a difference between the inputvoltage value of the power supply 250 obtained with the dividedresistors R211 and R212 and the reference voltage value e212 and thenoutputs such difference to the PWM comparator. When the input voltagevalue of power supply 250 is lowered, difference from the referencevoltage value e212 is reduced. Thereby, the error amplifier ERA12outputs a low level to reduce the charging power. Accordingly, a load ofthe external power supply 100 is reduced. When the input voltage valueof power supply 250 becomes high, difference from the reference voltagevalue e212 becomes large. Thereby, the error amplifier ERA212 outputs ahigh level.

[0122] This voltage comparator COMP201 is the circuit to compare theoutput voltage value of the error amplifier ERA211 for measuring acurrent to measure an output current value of the external power supply100 with the reference voltage value e31. The reference voltage valuee23 is identical to the maximum value of the output voltage value of thetriangular wave oscillating circuit 220. Similarly, the voltagecomparator COMP202 is the circuit to compare the output voltage value ofthe error amplifier ERA12 for measuring a voltage to measure the outputvoltage value of the external power supply 100.

[0123] Output signals of the voltage comparators COMP201 and COMP202 areOR'ed with a logical sum circuit OR201. The MASK1 signal becomes highlevel when the voltage comparator COMP201 or COMP202 outputs a highlevel. The MASK1 signal becomes a low level when both voltagecomparators COMP202 and COMP202 output low level.

[0124] Moreover, an output of the error amplifier ERA211 for currentmeasurement to measure the output current value of the external powersupply is outputted to the outside of the control section 215.Therefore, the microcomputer 213 can read the output current value ofthe external power supply.

[0125] The PWM comparator is a voltage comparator, as explained above,including one inverting input and a plurality of non-inverting inputs.The PWM comparator compares the lowest voltage value among a pluralityof inverting inputs with the voltage value of the inverted input. ThisPWM comparator is a voltage pulse width converter for controlling the ONtime of an output of the power supply depending on the input voltagevalue.

[0126] An output of the triangular wave oscillator is inputted to theinverting input of the PWM comparator. To the non-inverting inputs ofthe PWM comparator, outputs of the error amplifiers ERA221, ERA222,ERA211 and ERA212 are inputted. Therefore, the drive circuit 240 isdriven during the period where the triangular wave voltage from thetriangular oscillator 220 is lower than any voltage value of the outputvoltage values of the error amplifiers ERA221, ERA222, ERA211 andERA212. The drive circuit 240 drives the main switching FET1 (FIG. 11).

[0127] Moreover, the driving of the drive circuit 240 stops during theperiod where the voltage value of the triangular wave from thetriangular wave oscillator 220 is higher than any voltage value of theerror amplifiers ERA221, ERA222, ERA211 and ERA212. The drive circuit240 turns OFF the main switching FET1.

[0128] The input voltage value is measured with the resistors R221,R222. The measured input voltage value is then amplified with the erroramplifier ERA222 and is then inputted to the PWM comparator. To the PWMcomparator, the triangular wave from the triangular wave oscillator 220is applied. When the output voltage value of the error amplifier ERA222becomes large, an output pulse width of the PWM comparator also becomeslarge. When the output voltage value of the error amplifier ERA212becomes smaller, an output pulse width of the PWM comparator alsobecomes small. Therefore, when the input voltage value becomes small,the difference from the reference voltage value e22 becomes small. Anoutput voltage of the error amplifier ERA222 also becomes small.Therefore, the output pulse width of the PWM comparator becomes wide.When the input voltage value becomes large, the difference from thereference voltage value e222 becomes large. An output voltage of theerror amplifier ERA222 also becomes high. Therefore, the output pulsewidth of the PWM comparator becomes narrow.

[0129] As explained above, the power supply of the PWM control systemenables control of the output voltage by controlling the ON/OFF ratio(ratio of Ton and Toff) of the main switching FET1.

[0130]FIG. 16 is a graph illustrating the profile of the above describedcontrol for this power supply. The horizontal axis plots the time, whilethe vertical axis plots the voltage. In this figure, the output voltagevalue of the error amplifier ERA221 is always lower than the outputvoltage value of the error amplifier ERA222. Accordingly, when an outputof the PWM comparator is considered, it is enough to consider therelationship between the output voltage of the error amplifier ERA222and the voltage value of the triangular wave. After all, the PWMcomparator becomes ON when the output voltage value of the erroramplifier ERA222 is higher than the voltage value of triangular wave orbecomes OFF in other cases. As explained above, the PWM comparatoradjusts the output voltage by adjusting the output time.

[0131] Moreover, a total current of the current consumed in the loadside of the electronic device and a current consumed in the power supplyflows into the sense resistor R201 shown in FIG. 15 for measuring theconsumed current value of the electronic device. In case the powersupply 150 is replaced to power supply 250, a total current of thecurrent consumed in the load side of the electronic device and a currentconsumed in the power supply flows into the sense resistor R201 formeasuring the consumed current value of the electronic device. Voltagedrop generated by the current flowing through the sense resistor R201 isconverted to a voltage with the amplifier AMP211. The voltage value isamplified with the error amplifier ERA211 and is then inputted to thePWM comparator. To the PWM comparator, the triangular wave is appliedfrom the triangular wave oscillator and when the output voltage value ofthe error amplifier ERA211 becomes large, the output pulse width of thePWM comparator also becomes large. When the output voltage value of theerror amplifier ERA211 becomes small, the output pulse width of the PWMcomparator also becomes small.

[0132] Therefore, a total input current of the current consumed in theload side of the electronic device and the current consumed in thecharger is rather small, and the potential difference across the senseresistor R201 becomes small. Thereby, the difference between thepotential difference across the sense resistor R201 and the referencevoltage value e11 becomes large. The output voltage of the erroramplifier ERA211 becomes high. Therefore, the output pulse width of thePWM comparator becomes wide.

[0133] When an input current as a sum of the current consumed in theload side of the electronic device and the current consumed in thecharger becomes large, the voltage drop by the sense resistor R221becomes large. Thereby, the difference between the voltage dropgenerated with the sense resistor R221 and the reference voltage valuee211 becomes small. Here, the output voltage of the error amplifierERA211 also becomes lower. Thereby, the output pulse width of the PWMcomparator becomes narrow.

[0134]FIG. 17 illustrates how the PWM control system regulates outputcurrent by controlling the ON/OFF ratio (Ton to Toff ratio) of the mainswitching FET1. In the power supply control circuit operating asexplained above, when a load of the electronic device is rather light orwhen an output of the external power supply is sufficiently large thatis enough as the charging power of the secondary battery, the PWMcomparator is controlled with either the output voltage value of theerror amplifier ERA221 or the output voltage value of the erroramplifier ERA222 to control the output of the charger. The outputvoltage value of the error amplifier ERA211 for sensing the input of theexternal power supply and the output voltage value of the erroramplifier ERA212 do not take part in the control.

[0135] As a result, the output voltage value of the error amplifierERA211 and the output voltage value of the error amplifier ERA212 becomelarger than the maximum value of the voltage value of the triangularwave and the voltage comparators COMP201 and COMP202 output low levels.Therefore, the MASK1 and MASK2 signals are kept in the low level,indicating that the output of the external power supply is sufficient.

[0136] On the other hand, when the power consumption in the electronicdevice side and thereby a current flowing into the sense resistor R201for measuring current dissipation value also increases and reaches thepreset current value (set by the reference voltage source e211), thevoltage drop generated with the sense resistor R211 becomes large. Thedifference between the voltage drop generated with the sense resistorR211 and the reference voltage value e211 becomes small and the outputvoltage of the error amplifier ERA211 becomes lower. When the outputvoltage of the error amplifier ERA211 becomes lower, the output pulsewidth of the PWM comparator becomes narrow. If this condition occurs,the output voltage value of the error amplifier ERA211 becomes lowerthan the reference voltage value e23. As a result, the output of thevoltage comparator COMP201 becomes high level. An OR circuit 201 outputsthe high level.

[0137] On the other hand, since the output voltage of the external powersupply does not become lower, it does not take part in the control ofoutput of the power supply. The output voltage value of the erroramplifier ERA212 is high and is larger than the maximum value of thevoltage value of the triangular wave. Therefore, COMP202 outputs a lowlevel. As a result, the MASK1 signal becomes high level. The MASK2signal stays in the low level. Therefore, it indicates that the chargingcurrent of the secondary battery is limited due to the limitation of theoutput current of the external power supply.

[0138] Next, in another exemplary embodiment, the load of the externalpower supply is equal to the total power of the power consumption of thedocking station, power consumption of the electronic device and powerconsumption of the secondary battery. When the power consumption of theelectronic device side increases under this condition, a current flowinginto the sense resistor R212 to measure the current dissipation in theelectronic device side also increases. However, a load current in thedocking station side does not flow into the sense resistor R211.

[0139] As a result, the current value of the sense resistor R211 exceedsthe capacity of the external power supply in some cases before suchcurrent value reaches the preset current value (set with the referencevoltage source e211). In this case, the external power supply becomesoverloaded. In this case, since the external power supply drops theoutput voltage and therefore the output voltage of the error amplifierERA212 becomes lower and the output pulse width of the PWM comparatorbecomes narrow. Under the condition that the PWM comparator iscontrolled with the output voltage value of the error amplifier ERA212,the output voltage value of the error amplifier ERA212 becomes lowerthan the reference voltage value e231. As a result, the output of thevoltage comparator COMP202 becomes high level.

[0140] However, a current value flowing into the sense resistor R211does not reach the preset current value. The output voltage value of theerror amplifier ERA211 is kept higher than the reference voltage e31.The voltage comparator COMP201 outputs a low level. Therefore, althoughthe MASK1 signal is kept in the low level, the MASK2 signal becomes highlevel. This condition indicates that the charging current of thesecondary battery is limited with limitation of the output voltage ofthe external power supply.

[0141] Thus, an output voltage of the charger can be controlled for thepurpose that the output voltage of the external power supply does notdrop. The power supply control circuit is capable of dynamicallycontrolling the charging current depending on the capacity of theexternal power supply.

[0142] It is possible to know that the charging current of the secondarybattery is limited with limitation of output capacity of the externalpower supply from the MASK1 signal and MASK2 signal. Moreover, it isalso possible to identify that output capacity of the external powersupply is limited with the output current or with the output voltage.

[0143] Moreover, the output current of the external power supply can bedetected from an output of the voltage amplifier AMP211, since it flowsinto the sense resistor R211. The upper limit value of the currentflowing into the sense resistor R211 can be set with the referencevoltage source e211. In addition, the upper limit value of the chargingcurrent of the secondary battery built in the electronic device can alsobe set with the reference voltage source e212. The monitoring voltagevalue when the external power supply droops or drops the voltage underthe overload condition can also be set with the reference voltage sourcee221.

[0144] Although preferred embodiments of the present invention have beenshown and described, it will be appreciated by those skilled in the artthat changes may be made in these embodiments without departing from theprinciple and spirit of the invention, the scope of which is defined inthe appended claims and their equivalents.

What is claimed is:
 1. A power supply control circuit connectable withan input power monitor that monitors an input power value to a powersupply, an output power monitor that monitors an output power value fromthe power supply and an output power controller that varies the outputpower value from the power supply, the power supply control circuitcomprising: an output power determiner that determines a determinedoutput power value depending on the input power value; and a poweradjuster that adjusts the output power value to the determined outputpower value by controlling the output power controller.
 2. The powersupply control circuit as claimed in claim 1, wherein the output powerdeterminer determines, as the determined output value, a firstdetermined output power value that shows the input current value as afirst value and a second determined output power value that shows theinput current value as a second value smaller than the first value. 3.The power supply control circuit as claimed in claim 2, furthercomprising; a first timer that measures passage of a first time; asecond timer that measures passage of a second time after the firsttimer measures the first time; and an output power switch that instructsthe first value to the output power determining section while the firsttimer measures passage of the first time, and instructs the second valueto the output power determining section while the second timer measurespassage of the second time.
 4. The power supply control circuit asclaimed in claim 3, wherein the first time does not exceed two hours,and the second value is 0.8 or less of the first value.
 5. The powersupply control circuit as claimed in claim 1, further comprising: adeterminer that determines, in the event where an output power valuedoes not satisfy the predetermined value, whether the cause is in aninput voltage or the input current.
 6. The power supply control circuitas claimed in claim 1, wherein the input power monitor comprises: aresistor with two ends connected in a current flow of an input wiring;and wires connecting both ends of the resistor to the power supplycontrol circuit.
 7. The power supply control circuit as claimed in claim6, further comprising: an amplifier that measures a voltage drop acrossthe resistor and outputs a first voltage; and a comparator that comparesthe first voltage to a reference voltage and outputs a low level signalwhen the first voltage is high and outputs a high level signal when thefirst voltage is low.
 8. The power supply control circuit as claimed inclaim 1, wherein the power adjuster comprises: a comparator thatcompares the input power value and the output power value to thedetermined output power value to determine the adjustment to the outputpower controller.
 9. A power supply, comprising: an input power monitorthat monitors an input power value; an output power monitor thatmonitors an output power value; an output power controller that variesthe output power value by controlling an input current value; an outputpower determiner that determines a determined output power valuedepending on the input power value notified from the input powermonitor; and a power adjuster that maintains the output power valuenotified from the output power monitor as the determined output power bycontrolling the output power controller.
 10. The power supply as claimedin claim 9, wherein the output power determiner determines, as thedetermined output value, a first determined output power value thatshows the input current value as a first value and a second determinedoutput power value that shows the input current value as a second valuesmaller than the first value.
 11. The power supply as claimed in claim10, further comprising; a first timer that measures passage of a firsttime; a second timer that measures passage of a second time after thefirst timer measures the first time; and an output power switch thatinstructs the first value to the output power determining section whilethe first timer measures passage of the first time, and instructs thesecond value to the output power determining section while the secondtimer measures passage of the second time.
 12. The power supply asclaimed in claim 11, wherein the first time does not exceed two hours,and the second value is 0.8 or less of the first value.
 13. The powersupply as claimed in claim 9, wherein the controller comprises: adeterminer that determines, in the event where an output power valuedoes not satisfy the predetermined value, whether the cause is in aninput voltage or the input current.
 14. A power supply control methodcomprising: outputting a first output power value in which an inputcurrent value becomes a first value for a first time period bycontrolling the input current value so that an output power ismaintained as the first output power value; and outputting a secondoutput power value that is smaller than the first output power value fora second time period by controlling the input current value so that theoutput power is maintained as the second output power value.
 15. Thepower supply control method as claimed in claim 14, wherein the firsttime does not exceed two hours, and the second output power value is 0.8or less of the first value.
 16. The power supply control method asclaimed in claim 14, further comprising: determining, in the event wherean output power value does not satisfy the respective first or secondvalue, whether the cause is in an input voltage or input current.
 17. Anoutput power controller comprising: an output power determiner thatdetermines a determined output power value depending on an input powervalue; and a power adjuster that adjusts the output power value to thedetermined output power value by controlling an input current value. 18.The output power controller as claimed in claim 17, wherein the outputpower determiner determines, as the determined output value, a firstdetermined output power value that shows the input current value as afirst value and a second determined output power value that shows theinput current value as a second value smaller than the first value. 19.The output power controller as claimed in claim 18, further comprising;a first timer that measures passage of a first time; a second timer thatmeasures passage of a second time after the first timer measures thefirst time; and an output power switch that instructs the first value tothe output power determiner while the first timer measures passage ofthe first time, and instructs the second value to the output powerdeterminer while the second timer measures passage of the second time.20. The output power controller as claimed in claim 17, wherein thefirst time does not exceed two hours, and the second value is 0.8 orless of the first value.
 21. The output power controller as claimed inclaim 17, further comprising: a determiner that determines, in the eventwhere an output power value does not satisfy the predetermined value,whether the cause is in an input voltage or input current.